AeroElectric-Archive.digest.vol-ge
September 23, 2006 - October 02, 2006
> - Relays in some applications are less reliable than some solid state
>equivalents in that application. Saying hard/fast that relays are less
>reliable is probably not completely accurate.
>
> - When relays fail, often it's by degraded performance.. You'll notice
>that once in a while a relay will fail to snap in, or disconnect. You
>exercise the controlling switch a time or two, and it starts to function.
> You make the mental note "Hmmm, that xyz relay is getting flakey; better
>check it out when I get back to the hangar." And you go on with your
>flight.
>
> - The chances of a having a particular, properly installed/applied relay
>failing on any flight might be 1/10,000. The chances of having two
>different similar relays fail on the same flight might be 1/10,000 *
>1/10,000. A very unlikely possibility.
>
>
>Regards,
>
>Matt-
>
> > Bob, your 9/13/06 post regarding LEDs says in part:
> >
> >
> >
> > Finally, relays are rated amongst the least reliable of
> >
> > components. It behooves us to limit their use where ever practical.
> >
> >
> >
> > Okay. That brings up a question. I'm planning Z13/8 with Z32. Z32 Heavy
> > Duty E-Bus Feed shows the use of a relay to energize the alternate feed
> > path. But Z13/8 also relies on a relay to supply the SD-8's output to the
> > E-Bus. That's two relays that must work for E-Bus operations independent
> > of
> > battery power. Is there a practical way to avoid the built-in weakness of
> > two relays in the E-Bus circuit?
> >
> >
> >
> > John
> >
> >
>
>
________________________________________________________________________________
| From: | FLYaDIVE(at)aol.com |
| Subject: | Re: strange electrical failure in flight |
In a message dated 9/22/06 11:28:16 PM Eastern Daylight Time,
scc_ron(at)yahoo.com writes:
>
> Then I pulled the cowl to troubleshoot the problem. the master powered
up
> the Main bus as if nothing happened. I started the engine and got 13.5
volts
> from the ND Alternator regardless of RPM. When I switched on the E Bus, the
> charge rate / output from the alternator jumped to 14.3. If I switched it
off,
> the number again drops back to 13.5 volts. No blown fuses.
>
> Anybody have an idea of what happened and what I might want to do?
Thanks
> in advance.
> Ron
> RV-4 N8ZD
==========================
Ron:
It sure sounds like a bad GROUND. Second guess would be a bad B+ connection.
But, start with the GROUND, that is easy to check just by hooking a ground
wire to the battery and bypassing to the other ground connection points.
Been there, Done that. And POOF the problem was gone.
Barry
"Chop'd Liver"
"Show them the first time, correct them the second time, kick them the third
time."
Yamashiada
________________________________________________________________________________
| From: | Kevin Horton <khorton01(at)rogers.com> |
| Subject: | Re: strange electrical failure in flight |
On 22 Sep 2006, at 23:25, Ron Patterson wrote:
> Hope someone has some ideas on how to troubleshoot an eletrical
> failure that I don't understand. I have Bob's Essential Bus and
> Main Bus setup, one battery, new plane (50 hours). In flight today
> I had an indication that I had a problem when my main bus connected
> items shut down. I turned on the Essential bus, turned off the
> Cessna type Master/Battery switch and continued on, landing
> uneventfully as planned with Bob's system.
>
> Then I pulled the cowl to troubleshoot the problem. the master
> powered up the Main bus as if nothing happened. I started the
> engine and got 13.5 volts from the ND Alternator regardless of RPM.
> When I switched on the E Bus, the charge rate / output from the
> alternator jumped to 14.3. If I switched it off, the number again
> drops back to 13.5 volts. No blown fuses.
>
> Anybody have an idea of what happened and what I might want to do?
> Thanks in advance.
Don't worry about the difference in indicated voltage when you switch
the E Bus on and off. Your voltmeter is connected to the E Bus,
which is normally supplied from the Main Bus, through a diode. The
difference in voltages you see when the E Bus is switched on and off
is due to the voltage drop through the diode. This is normal.
In flight, did all the electrically powered items die at the same
time? If so, it looks like something happened that killed the power
supply to the Main Bus. Is your system wired so the normal feed to
the Main Bus comes from the starter contactor, with the battery
contactor and alternator feed also connected to that same bolt on the
starter contactor? If so, check the connection there, and at the
other end of that cable where it connects to the Main Bus.
If the electrically powered items failed one by one, then it sounds
like a low voltage condition, due to an alternator problem. Let us
know if this was the way things happened and we can work this avenue.
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://www.kilohotel.com/rv8
________________________________________________________________________________
| From: | Richard Reynolds <rvreynolds(at)macs.net> |
| Subject: | Re: strange electrical failure in flight |
Because of the diode between the main and essential buses, there will
be a lower voltage on the essential bus with the essential bus switch
off if voltage is measured on the essential bus..
The best place to measure the charing voltage is at the alternaor
side of the starter contactor or the battery contactor or the battery.
Where are you measuring the voltage?
Richard Reynolds
Norfolk VA
On Sep 22, 2006, at 11:25 PM, Ron Patterson wrote:
> Hope someone has some ideas on how to troubleshoot an eletrical
> failure that I don't understand. I have Bob's Essential Bus and
> Main Bus setup, one battery, new plane (50 hours). In flight today
> I had an indication that I had a problem when my main bus connected
> items shut down. I turned on the Essential bus, turned off the
> Cessna type Master/Battery switch and continued on, landing
> uneventfully as planned with Bob's system.
>
> Then I pulled the cowl to troubleshoot the problem. the master
> powered up the Main bus as if nothing happened. I started the
> engine and got 13.5 volts from the ND Alternator regardless of RPM.
> When I switched on the E Bus, the charge rate / output from the
> alternator jumped to 14.3. If I switched it off, the number again
> drops back to 13.5 volts. No blown fuses.
>
> Anybody have an idea of what happened and what I might want to do?
> Thanks in advance.
> Ron
> RV-4 N8ZD
>
>
________________________________________________________________________________
| From: | MikeEasley(at)aol.com |
| Subject: | Ground Power Jack Question |
I installed the Ground Power Jack according to the article. I built jumper
cables from some Harbor Freight "el cheapo" cables and a plug from A/S. I
tried to hook up my battery charger to the jumper cables and charge my battery
but the contactor won't close. It appears that my charger won't put out any
current unless it "senses" a battery is connected. If I hook my jumper
cables to a spare car battery, everything works fine.
Mike Easley
Colorado Springs
Lancair ES 12V
________________________________________________________________________________
| From: | Gary Casey <glcasey(at)adelphia.net> |
| Subject: | Re: Mogas versus 100LL |
Good comments, Ron. Yes, the octane rating is a measure of the
resistance of the fuel/air mixture to auto-ignite, or ignite without
the presence of an open flame. It's a complex phenomenon and
autoignition is a function of time, pressure and temperature. The
rating methodology, developed by Ethyl Corporation way back when,
compares the resistance to auto-ignition of the test fuel to mixtures
of normal heptane to iso-octane. The octane number is the percentage
of iso-octane in the mix that behaves like the test fuel (80-octane
fuel behaves like a a mixture of 20% n-heptane and 80% iso-octane).
Since the actual test is really done by measuring the BMEP of a test
engine, numbers over 100 are possible - 110-octane fuel will allow
the test engine to operate at 110% of the BMEP allowed by iso-octane
(not exactly correct, but close enough). The method isn't exact and
if the test engine is operated at different temperatures and loads
the observed octane number comes out differently. Running at light
load creates an octane rating called the "research octane" number and
running at high temperature/high load produces a number called "motor
octane". The law says the average octane rating of an automotive
fuel must be displayed on the pump and that's why it says (R+M)/2 on
the pump. Aviation fuel, because engines are usually operated under
conditions more like the the motor method, are typically rated by the
motor method - I believe 100LL is more correctly called 100/120 (100
motor octane and 120 research octane). That's why some of the past-
history fuels were called 110/130 etc.
When the fuel is ignited by an open flame front there is little
difference in flame speed between high octane and low octane fuel:
Flame speed is NOT the primary difference between the fuels.
Detonation is auto-ignition of the "end gases" late in the combustion
process. Because of combustion in the cylinder the end gases(the
portion of the charge furthest from the ignition source) are
compressed to very high pressures, which because of the gas law
PV=NRT, raises their temperature. They will only remain unburned for
a limited time and if the flame front doesn't arrive soon enough,
igniting them progressively, they will auto-ignite all at once,
"exploding." This will cause all sorts of problems, but will not
usually result in immediate engine failure.
As Ron correctly described below, "pre-ignition" is simply ignition
of the fuel charge before the spark occurs. Because the charge burns
and raises the pressure before the piston fully compresses the charge
the temperature and pressure can go to extremely high levels, causing
major damage very quickly. For example (George Braly would have the
real numbers) normal compression (no ignition) pressure might be
350psi, combustion results in pressures of 800 to 1,000 psi and pre-
ignition could result in pressures up to 2,000 psi. Pre-ignition can
(likely) result from pre-ignition because of the extremely high
pressure and temperature of the end gases. One thing that isn't
usually thought about is the rate of heat transfer from a gas to the
cylinder, which is proportional to the velocity, temperature
difference AND PRESSURE of the gas. Double the pressure and double
the temperature and the heat transfer will go up by a factor of 4.
Detonation results in sonic shock waves traveling through the
combustion chamber, which means locally the hot gases are moving at
sonic velocity. Much of the damage from both detonation and pre-
ignition is caused by the extremely high heat transfer rates, not
just the pressure. Detonation under high loads can increase the
local heat transfer rate to the point that after a short time a
component (edge of the exhaust valve, carbon deposit, etc) can be
heated to the point it causes pre-ignition. This has sometimes been
referred to as "runaway detonation."
I hope from the above description you get the idea that detonation
and pre-ignition can be a real horror story for the engine. The best
thing is to maintain a healthy detonation margin. In general,
detonation is suppressed by increasing the octane rating, lowering
the compression ratio, retarding the ignition timing, lowering the
inlet temperature and pressure, lowering the cylinder head
temperature, increasing turbulence and reducing the distance from the
spark plug to the end gases(by running on both plugs). And you can
dilute the charge by adding water, excess fuel or excess air (run
LOP). As you can see, most of these things will reduce the power
output of the engine and therein lies the conundrum. For a standard
unmodified aircraft engine the worst operating case would be a
takeoff from Death Valley on a dry, 115-degree day with the carb heat
left on, mixture leaned and one of the mags inoperative. As I recall
it is just those conditions that the FAA requires to be demonstrated
for a certified engine.
Sorry about the excessively long non-electric dissertation.
Gary Casey
> The higher the octane rating, the higher the temperature and
> pressure that can be reached before detonation occurs. I am not
> positive
> on this, but am pretty certain on Mainland USA, the pump octane rating
> is
> not figured the same as Aviation fuel is, I forget if Avgas is
> higher or
> lower. Anyway for a short time detonation probably will not cause any
> real
> harm. Now if you let it go on for long periods of time, things will
> begin
> to heat up, detonation will become more pronounced. The burning of
> fuel
> mixture during Detonation begins with a spark at the plug. Preignition
> is
> the real show stopper. This is where for some reason the mixture
> ignites
> way too far advanced. Could be a glowing piece of carbon, or
> leaving the
> helicoil tab stick a bit too much into the cylinder, or just plain too
> high a temperature. Piston moving up and fighting pressure now.
>
> OK comments here??
>
> OK so if we are straight that octane rating is the ability for a
> fuel to
> not detonate, I don't think that is absolute takes into consideration
> the
> speed at which the flame front will burn in an orderly fashion.
> Different
> brews can have the same octane rating, but can burn at different
> speeds.
> Ron Parigoris
________________________________________________________________________________
| From: | "John Swartout" <jgswartout(at)earthlink.net> |
| Subject: | Eeeeek! Another fear and question. |
Well, I'm trying to understand the system I'm going to install, and some
things aren't making sense to me.
Following your reasoning, since I spent big bucks on a highly reliable
L40
main alternator which doesn't rely on any relay to deliver power, and on
two
P-mags which may not require any ship's power anyway, the highly
reliable
SD-8 backup alternator is just excess baggage so what difference does it
make whether its electrons can get to where they are needed? That
doesn't
sound like correct design theory to me.
I am trying to integrate Z-13/8, Z-32, and an avionics master switch
circuit
of Bob's design, and am trying to figure out where and whether to use
relays
which are shown in Z-32 but not in the other drawings. I note that in
Z-32,
the up-to-8-amp Endurance Bus feeds alternate power through a relay.
(Bob
has a sketch at
www.aeroelectric.com/Pictures/Schematics/E-BusFatFeed.gif
which says "for [E-Bus] feeds over 5A consider adding a relay to control
power at the Bat Bus.") I seem to recall that the reason for using a
relay
is to avoid arcing at the switch which would possibly compromise the
switch.
But in Bob's article "Avionics Master Switches: Really Necessary?," he
shows a circuit with the caption "If you really want an avionics master
switch, how about doing it this way?" It shows an essential
bus/avionics
bus powering a transponder, turn coordinator, intercom, instrument
flood,
gps receiver, Nav/Comm, and fuel boost pump. Both the main feed and the
alternate feed are controlled by switches, not relays. I like the idea
and
want to use it-but my endurance/avionics bus supports more than 5 amps,
so I
am "considering" the Z-32 Heavy Duty E-Bus, which uses a relay. This
made
me think, if the alternate feed needs a relay, shouldn't the main feed
(avionics master switched) use a relay also? If not, why not? It's
doing
the same thing normally that the alternate feed does if the main
alternator
fails-so why doesn't it need a relay, too? But Bob's recent post saying
that relays are among the least reliable of components makes me nervous
because in the combined schematic I am contemplating my Endurance Bus
would
be dependent on one relay in normal mode and two relays if I were
operating
in main-alternator-failed mode. Remember that the "Endurance Bus" used
to
be named the "Essential Bus" (for a legitimate reason). Should anything
"Essential" really be totally dependent on relays? If not, I am looking
for
assistance in developing a better architecture that gives me a Heavy
Duty
(up to 8-amp) Essential/Avionics Bus with an avionics master switch.
John
-----Original Message-----
From: owner-aeroelectric-list-server(at)matronics.com
[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Dave
N6030X
Sent: Friday, September 22, 2006 11:34 PM
Subject: RE: AeroElectric-List: Eeeeek! Another fear and question.
I think that's why it's called the Endurance Bus. So what if both
relays fail. If you've designed the system correctly, you have
sufficient battery to get to your destination, and you don't even
break a sweat.
Dave Morris
At 10:15 PM 9/22/2006, you wrote:
>
>
>I *assume* that while relays may be the "least reliable" of components,
they
>are still "pretty" reliable, else they would not appear in the
Z-drawings.
>But my point is that when you combine Z13/8 and Z32, the chances of the
>E-bus not working in a main-alternator-failure situation are not your
>hypothetical 1/10,000 * 1/10,000, rather they are increased to 1/5,000
>because BOTH relays have to work, and if either one fails (1/10,000 *
2)
you
>are flying on the battery only, even though the SD-8 is fine. Usually
Bob
>endeavors to minimize the opportunities for a single component failure
to
>cause an emergency, and I wonder if he considers this daisy chain of
"least
>reliable components" in the Z13/8 + Z32 to pass muster.
>
>John
>
>-----Original Message-----
>From: owner-aeroelectric-list-server(at)matronics.com
>[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Matt
>Prather
>Sent: Friday, September 22, 2006 7:30 PM
>To: aeroelectric-list(at)matronics.com
>Subject: Re: AeroElectric-List: Eeeeek! Another fear and question.
>
>
>A couple of thoughts...
>
> - Relays in some applications are less reliable than some solid state
>equivalents in that application. Saying hard/fast that relays are less
>reliable is probably not completely accurate.
>
> - When relays fail, often it's by degraded performance.. You'll
notice
>that once in a while a relay will fail to snap in, or disconnect. You
>exercise the controlling switch a time or two, and it starts to
function.
> You make the mental note "Hmmm, that xyz relay is getting flakey;
better
>check it out when I get back to the hangar." And you go on with your
>flight.
>
> - The chances of a having a particular, properly installed/applied
relay
>failing on any flight might be 1/10,000. The chances of having two
>different similar relays fail on the same flight might be 1/10,000 *
>1/10,000. A very unlikely possibility.
>
>
>Regards,
>
>Matt-
>
> > Bob, your 9/13/06 post regarding LEDs says in part:
> >
> >
> >
> > Finally, relays are rated amongst the least reliable of
> >
> > components. It behooves us to limit their use where ever
practical.
> >
> >
> >
> > Okay. That brings up a question. I'm planning Z13/8 with Z32. Z32
Heavy
> > Duty E-Bus Feed shows the use of a relay to energize the alternate
feed
> > path. But Z13/8 also relies on a relay to supply the SD-8's output
to
the
> > E-Bus. That's two relays that must work for E-Bus operations
independent
> > of
> > battery power. Is there a practical way to avoid the built-in
weakness
of
> > two relays in the E-Bus circuit?
> >
> >
> >
> > John
> >
> >
>
>
>
>
>
>
>
>
________________________________________________________________________________
| From: | Dave N6030X <N6030X(at)DaveMorris.com> |
| Subject: | Eeeeek! Another fear and question. |
Well, I'll wait for Bob to justify his own
schematics, but I know he is in Kansas at the
tandem-wing fly-in today and may not be able to comment for a while.
If it were ME, I would not use a relay to power
the E-bus. I would use a switch. Switches
handle larger current than 5A all the time, and
if you're concerned about reliability, just use a
switch rated for larger current. The other thing
you should do here, since you're discovering you
have an unusual e-bus, is to ask yourself whether
all of those items really need to be on the
e-bus. I had to go through several iterations
before I finally pared my e-bus down to what was
really going to be necessary to have running ALL
THE TIME to complete the flight. Remember you
can always power up the Main Bus for a few
minutes if you need to, while on battery power.
Dave Morris
At 09:14 AM 9/23/2006, you wrote:
>Well, I'm trying to understand the system I'm
>going to install, and some things aren't making sense to me.
>
>Following your reasoning, since I spent big
>bucks on a highly reliable L40 main alternator
>which doesn't rely on any relay to deliver
>power, and on two P-mags which may not require
>any ship's power anyway, the highly reliable
>SD-8 backup alternator is just excess baggage so
>what difference does it make whether its
>electrons can get to where they are
>needed? That doesn't sound like correct design theory to me.
>
>I am trying to integrate Z-13/8, Z-32, and an
>avionics master switch circuit of Bobs design,
>and am trying to figure out where and whether to
>use relays which are shown in Z-32 but not in
>the other drawings. I note that in Z-32, the
>up-to-8-amp Endurance Bus feeds alternate power
>through a relay. (Bob has a sketch at
><http://www.aeroelectric.com/Pictures/Schematics/E-BusFatFeed.gif>www.aeroelectric.com/Pictures/Schematics/E-BusFatFeed.gif
>which says for [E-Bus] feeds over 5A consider
>adding a relay to control power at the Bat
>Bus.) I seem to recall that the reason for
>using a relay is to avoid arcing at the switch
>which would possibly compromise the switch.
>
>But in Bobs article Avionics Master
>Switches: Really Necessary?, he shows a
>circuit with the caption If you really want an
>avionics master switch, how about doing it this
>way? It shows an essential bus/avionics bus
>powering a transponder, turn coordinator,
>intercom, instrument flood, gps receiver,
>Nav/Comm, and fuel boost pump. Both the main
>feed and the alternate feed are controlled by
>switches, not relays. I like the idea and want
>to use itbut my endurance/avionics bus supports
>more than 5 amps, so I am considering the Z-32
>Heavy Duty E-Bus, which uses a relay. This made
>me think, if the alternate feed needs a relay,
>shouldnt the main feed (avionics master
>switched) use a relay also? If not, why
>not? Its doing the same thing normally that
>the alternate feed does if the main alternator
>failsso why doesnt it need a relay, too? But
>Bobs recent post saying that relays are among
>the least reliable of components makes me
>nervous because in the combined schematic I am
>contemplating my Endurance Bus would be
>dependent on one relay in normal mode and two
>relays if I were operating in
>main-alternator-failed mode. Remember that the
>Endurance Bus used to be named the Essential
>Bus (for a legitimate reason). Should anything
>Essential really be totally dependent on
>relays? If not, I am looking for assistance in
>developing a better architecture that gives me a
>Heavy Duty (up to 8-amp) Essential/Avionics Bus with an avionics master switch.
>
>John
>
>-----Original Message-----
>From:
>owner-aeroelectric-list-server(at)matronics.com
>[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Dave N6030X
>Sent: Friday, September 22, 2006 11:34 PM
>To: aeroelectric-list(at)matronics.com
>Subject: RE: AeroElectric-List: Eeeeek! Another fear and question.
>
>
>I think that's why it's called the Endurance Bus. So what if both
>relays fail. If you've designed the system correctly, you have
>sufficient battery to get to your destination, and you don't even
>break a sweat.
>
>Dave Morris
>
>At 10:15 PM 9/22/2006, you wrote:
> >
> >
> >I *assume* that while relays may be the "least reliable" of components, they
> >are still "pretty" reliable, else they would not appear in the Z-drawings.
> >But my point is that when you combine Z13/8 and Z32, the chances of the
> >E-bus not working in a main-alternator-failure situation are not your
> >hypothetical 1/10,000 * 1/10,000, rather they are increased to 1/5,000
> >because BOTH relays have to work, and if either one fails (1/10,000 * 2) you
> >are flying on the battery only, even though the SD-8 is fine. Usually Bob
> >endeavors to minimize the opportunities for a single component failure to
> >cause an emergency, and I wonder if he considers this daisy chain of "least
> >reliable components" in the Z13/8 + Z32 to pass muster.
> >
> >John
> >
> >-----Original Message-----
> >From: owner-aeroelectric-list-server(at)matronics.com
> >[mailto:owner-aeroelectric-list-server(at)matronics.com] On Behalf Of Matt
> >Prather
> >Sent: Friday, September 22, 2006 7:30 PM
> >To: aeroelectric-list(at)matronics.com
> >Subject: Re: AeroElectric-List: Eeeeek! Another fear and question.
> >
> >
> >A couple of thoughts...
> >
> > - Relays in some applications are less reliable than some solid state
> >equivalents in that application. Saying hard/fast that relays are less
> >reliable is probably not completely accurate.
> >
> > - When relays fail, often it's by degraded performance.. You'll notice
> >that once in a while a relay will fail to snap in, or disconnect. You
> >exercise the controlling switch a time or two, and it starts to function.
> > You make the mental note "Hmmm, that xyz relay is getting flakey; better
> >check it out when I get back to the hangar." And you go on with your
> >flight.
> >
> > - The chances of a having a particular, properly installed/applied relay
> >failing on any flight might be 1/10,000. The chances of having two
> >different similar relays fail on the same flight might be 1/10,000 *
> >1/10,000. A very unlikely possibility.
> >
> >
> >Regards,
> >
> >Matt-
> >
> > > Bob, your 9/13/06 post regarding LEDs says in part:
> > >
> > >
> > >
> > > Finally, relays are rated amongst the least reliable of
> > >
> > > components. It behooves us to limit their use where ever practical.
> > >
> > >
> > >
> > > Okay. That brings up a question. I'm
> planning Z13/8 with Z32. Z32 Heavy
> > > Duty E-Bus Feed shows the use of a relay to energize the alternate feed
> > > path. But Z13/8 also relies on a relay to
> supply the SD-8's output to the
> > > E-Bus. That's two relays that must work for E-Bus operations independent
> > > of
> > > battery power. Is there a practical way to
> avoid the built-in weakness of
> > > two relays in the E-Bus circuit?
> > >
> > >
> > >
> > > John
> > >
> > >
> >
> >
> >
> >
> >
> >
> >
> >
>
>
________________________________________________________________________________
| From: | "Robert L. Nuckolls, III" <nuckollsr(at)cox.net> |
| Subject: | Re: Eeeeek! Another fear and question. |
>Bob, your 9/13/06 post regarding LEDs says in part:
>
>
>Finally, relays are rated amongst the least reliable of
>
> components. It behooves us to limit their use where ever practical.
>
>
>Okay. That brings up a question. I m planning Z13/8 with Z32. Z32 Heavy
>Duty E-Bus Feed shows the use of a relay to energize the alternate feed
>path. But Z13/8 also relies on a relay to supply the SD-8 s output to the
>E-Bus. That s two relays that must work for E-Bus operations independent
>of battery power. Is there a practical way to avoid the built-in weakness
>of two relays in the E-Bus circuit?
This thread has expanded into a predictable level of
excitement for lack of perspective . . .
Note the key word in the quotation above . . . PRACTICAL
About 20 years ago, I was designing the first of a series
of electronically controlled rate controllers for
pitch trim on the Learjets. While conducting a Mil-HBK-217
MTBF study, it was interesting to note that when only
the electronic components, wires, solder joints and connectors
were factored into the study, MTBF for the device was in
the thousands of hours . . . about 7,000 as I recall.
When adding the last component, a mil-spec, 4-pole, double
throw, hermetically sealed 25A relay to the study, the predicted
MTBF fell to 900 hours for the system.
Mil-HBK-217 suggests and even accommodates de-rating of
parts to decrease stresses with commensurate increases in
MTBF. I was able to design the system so that the relay
was closed and bounce free before current flowed in the
contacts. Further, I was able to shut off all current flow
electronically before the relay contacts were opened.
Mil-HDK-217 had no prediction formula for my proposed scenario
but obviously, it was going to be as high as was PRACTICALLY
possible for incorporation of the relay. Twenty years later,
inquiries to the overhaul shop for this product tell me that
relays have NEVER been replaced in a unit returned for repair.
Even as I write these words, I'm designing the next new
product to appear in the AeroElectric Connection catalog
and the design incorporates a RELAY. Why not replace it
electronically? PRACTICALITY - it's technologically possible
but costs more . . . makes the product more expensive to
build and doesn't make it perform any better. It MIGHT
keep the system from needing maintenance attention before
the original owner sells the airplane . . . but I doubt
it.
The decision as to whether a relay or contactor is
PRACTICAL involves consideration of much more data than
the gross reliability factors. Cost of ownership and
FMEA for the SYSTEM figure heavily into the thought
process. We still use $25, el-cheeso contactors in our
airplanes because in spite of their need for periodic
maintenance, we have crafted a Plan-B to deal with those
failures. Hence my recommendation to many builders over
the years that 'upgrading' to Mil-Spec contactors in
their RV is dollars probably not well spent.
So before anyone goes of the end of the plank in
excitement or fear, know that suggestions for the
selection of ANY component need to be considered against
your ability to deal sweat-free with a failure of that
component. If your Plan-B is solid, then use of that
component is PRACTICAL and as free of excitement and
concerns as we know how to do.
Bob . . .
________________________________________________________________________________
| From: | "Robert L. Nuckolls, III" <nuckollsr(at)cox.net> |
| Subject: | Re: Ground Power Jack Question |
>I installed the Ground Power Jack according to the article. I built
>jumper cables from some Harbor Freight "el cheapo" cables and a plug from
>A/S. I tried to hook up my battery charger to the jumper cables and
>charge my battery but the contactor won't close. It appears that my
>charger won't put out any current unless it "senses" a battery is
>connected. If I hook my jumper cables to a spare car battery, everything
>works fine.
>
>Mike Easley
>Colorado Springs
>Lancair ES 12V
Yup, some chargers are like that. You might need to 'float'
a small battery across the charger terminals external to the
airplane to wake it up so that you can get power to the
ship's battery for charging.
Understand further that having a fixed, external power
contactor's coil load on a 'smart charger' will probably prevent
it from going into the maintenance mode when ship's battery
achieves full charge.
Smart chargers should be fitted with low current, fused
feeders directly to the battery bus. A connector set like
http://www.aeroelectric.com/Pictures/Connectors/274-010.jpg
http://www.aeroelectric.com/Pictures/Connectors/274-013.jpg
might do nicely. These parts are available from Radio Shack.
Bob . . .
---------------------------------------------------------
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
---------------------------------------------------------
________________________________________________________________________________
| From: | "Robert L. Nuckolls, III" <nuckollsr(at)cox.net> |
| Subject: | Eeeeek! Another fear and question. |
>
>Well, I'll wait for Bob to justify his own schematics, but I know he is in
>Kansas at the tandem-wing fly-in today and may not be able to comment for
>a while.
>
>If it were ME, I would not use a relay to power the E-bus. I would use a
>switch. Switches handle larger current than 5A all the time, and if
>you're concerned about reliability, just use a switch rated for larger
>current. The other thing you should do here, since you're discovering you
>have an unusual e-bus, is to ask yourself whether all of those items
>really need to be on the e-bus. I had to go through several iterations
>before I finally pared my e-bus down to what was really going to be
>necessary to have running ALL THE TIME to complete the flight. Remember
>you can always power up the Main Bus for a few minutes if you need to,
>while on battery power.
>
>Dave Morris
The suggestion for adding an e-bus relay had nothing to do
with current carrying capacity of the e-bus switch. There's
be a long standing tradition in TC aircraft to limit the size
of always-hot feeders in aircraft to those protected by 5A or
smaller breakers.
Since the "FAT" e-bus feeder needs to carry more than the few
amps originally considered when the e-bus was conceived, the
idea for adding a 'mini-contactor' at the e-bus for larger
feeders was offered.
Now, fuses are much faster than breakers, and for Z-13/8
were a continuous e-bus load of 8A is PRACTICAL, then
assuming the e-bus alternate feed is fuse-fed from the
battery bus, going up to 10A fuse is a useful thing to
consider without thumbing our noses too vigorously at tradition.
Too many folks are treating the Z-figures as carved-in-
stone recommendations for details of a proposed electrical
system. These drawings are STARTING POINTS that illustrate
architectures that will in-turn drive your Plan-A/Plan-B
thinking.
Don't get yourselves wrapped around any axles here based
on sizes of wires, sizes of fuses/breakers or which
devices are fed from which busses. The drawings were
never intended to be a recipe for success, only a tool
for development. I get a half-dozen requests a week for
"Gee Bob, I like Figure Z-x but it doesn't . . . and
I want to . . . Would you please craft me a Z-y that
takes care of all my desires/worries?"
All these requests get the same reply which is not
much different that what I've written above. Nobody
promised anyone a decision free solution. One is
always on firm footing to clone the system out of
a C-172 and drive on. Any variations from that theme
WILL require thought, exploration, crafting/answering
of questions and finally understanding of the final
configuration which WILL be uniquely applicable to
YOU and your airplane.
Bob . . .
________________________________________________________________________________
| From: | Vern Little <rv-9a-online(at)telus.net> |
| Subject: | Re: strange electrical failure in flight |
Ron, did you measure the alternator output voltage directly at the
battery, or is your voltmeter connected to the main bus?
If you have any isolation diodes involved between the voltmeter and the
battery (such as automatic e-bus/main bus switching), this could be the
cause of your 13.5 volt reading.
Vern Little
Ron Patterson wrote:
> Hope someone has some ideas on how to troubleshoot an eletrical failure
> that I don't understand. I have Bob's Essential Bus and Main Bus setup,
> one battery, new plane (50 hours). In flight today I had an indication
> that I had a problem when my main bus connected items shut down. I
> turned on the Essential bus, turned off the Cessna type Master/Battery
> switch and continued on, landing uneventfully as planned with Bob's system.
>
> Then I pulled the cowl to troubleshoot the problem. the master powered
> up the Main bus as if nothing happened. I started the engine and got
> 13.5 volts from the ND Alternator regardless of RPM. When I switched on
> the E Bus, the charge rate / output from the alternator jumped to 14.3.
> If I switched it off, the number again drops back to 13.5 volts. No
> blown fuses.
>
> Anybody have an idea of what happened and what I might want to do?
> Thanks in advance.
> Ron
> RV-4 N8ZD
>
> *
>
>
> *
________________________________________________________________________________
| From: | "DAVID REEL" <dreel(at)cox.net> |
| Subject: | Re: strange electrical failure in flight |
The big increase in voltage with load could be due to high resistance in the
regulator sense circuit. The more load you add, the higher the current in
the alternator field coil. If the sense circuit is also the field coil
supply, any resistance in the circuit will cause a voltage drop and the
regulator will increase the voltage to make up for the sensed drop in
voltage. So, if you add lots of load, you could be getting voltage spikes
over 16v which would trip an overvoltage protector which you probably also
have. Check to see if your alternator field circuit breaker tripped.
I had to reduce the resistance in my field circuit to .02 ohms by removing
the fuse and wiring it directly to the buss through a fuse link before I
could get reliable operation from my system.
Dave Reel - RV8A
________________________________________________________________________________
| From: | "n801bh(at)netzero.com" <n801bh(at)NetZero.com> |
| Subject: | Re: Mogas versus 100LL |
Thank you Gary. That is the best explanation of octane and detonation/ p
reignition scenerios I have ever read. I was going to try to desrcibe it
but you did so much better. The only thing I might add is the fact that
in the process of diluting the mixture with extra air there is a point
where before it really starts to run lean the engine flame front goes in
to a blow torch effect and will melt the top of the piston and or the ex
haust valve. If you can transition though this setting fast enough the m
otor just lays down and the EGT's show a cooler number, set the air/fuel
mixture at around 16-1, depending on the engine of course, and work the
motor hard, you will get very high EGT's, low fuel flow numbers and hur
t pistons/ valves. The best way to describe it is watch a cutting torch
work, one adjusts the mixture till they get a neutral flame and when yo
u press the lever the additional O2 will not only add to the velocity of
the flame front , it will almost double the temp of the cutting flame i
tself. .
Ben
www.haaspowerair.com
Ben Haas
N801BH
www.haaspowerair.com
-- Gary Casey wrote:
Good comments, Ron. Yes, the octane rating is a measure of the resistan
ce of the fuel/air mixture to auto-ignite, or ignite without the presenc
e of an open flame. It's a complex phenomenon and autoignition is a fun
ction of time, pressure and temperature. The rating methodology, develo
ped by Ethyl Corporation way back when, compares the resistance to auto-
ignition of the test fuel to mixtures of normal heptane to iso-octane.
The octane number is the percentage of iso-octane in the mix that behave
s like the test fuel (80-octane fuel behaves like a a mixture of 20% n-h
eptane and 80% iso-octane). Since the actual test is really done by mea
suring the BMEP of a test engine, numbers over 100 are possible - 110-oc
tane fuel will allow the test engine to operate at 110% of the BMEP allo
wed by iso-octane(not exactly correct, but close enough). The method is
n't exact and if the test engine is operated at different temperatures a
nd loads the observed octane number comes out differently. Running at l
ight load creates an octane rating called the "research octane" number a
nd running at high temperature/high load produces a number called "motor
octane". The law says the average octane rating of an automotive fuel
must be displayed on the pump and that's why it says (R+M)/2 on the pump
. Aviation fuel, because engines are usually operated under conditions
more like the the motor method, are typically rated by the motor method
- I believe 100LL is more correctly called 100/120 (100 motor octane and
120 research octane). That's why some of the past-history fuels were c
alled 110/130 etc.
When the fuel is ignited by an open flame front there is little differen
ce in flame speed between high octane and low octane fuel: Flame speed
is NOT the primary difference between the fuels. Detonation is auto-ign
ition of the "end gases" late in the combustion process. Because of com
bustion in the cylinder the end gases(the portion of the charge furthest
from the ignition source) are compressed to very high pressures, which
because of the gas law PV=NRT, raises their temperature. They will on
ly remain unburned for a limited time and if the flame front doesn't arr
ive soon enough, igniting them progressively, they will auto-ignite all
at once, "exploding." This will cause all sorts of problems, but will n
ot usually result in immediate engine failure.As Ron correctly described
below, "pre-ignition" is simply ignition of the fuel charge before the
spark occurs. Because the charge burns and raises the pressure before t
he piston fully compresses the charge the temperature and pressure can g
o to extremely high levels, causing major damage very quickly. For exam
ple (George Braly would have the real numbers) normal compression (no ig
nition) pressure might be 350psi, combustion results in pressures of 800
to 1,000 psi and pre-ignition could result in pressures up to 2,000 psi
. Pre-ignition can (likely) result from pre-ignition because of the ext
remely high pressure and temperature of the end gases. One thing that i
sn't usually thought about is the rate of heat transfer from a gas to th
e cylinder, which is proportional to the velocity, temperature differenc
e AND PRESSURE of the gas. Double the pressure and double the temperatu
re and the heat transfer will go up by a factor of 4. Detonation result
s in sonic shock waves traveling through the combustion chamber, which m
eans locally the hot gases are moving at sonic velocity. Much of the da
mage from both detonation and pre-ignition is caused by the extremely hi
gh heat transfer rates, not just the pressure. Detonation under high lo
ads can increase the local heat transfer rate to the point that after a
short time a component (edge of the exhaust valve, carbon deposit, etc)
can be heated to the point it causes pre-ignition. This has sometimes b
een referred to as "runaway detonation."I hope from the above descriptio
n you get the idea that detonation and pre-ignition can be a real horror
story for the engine. The best thing is to maintain a healthy detonati
on margin. In general, detonation is suppressed by increasing the octan
e rating, lowering the compression ratio, retarding the ignition timing,
lowering the inlet temperature and pressure, lowering the cylinder head
temperature, increasing turbulence and reducing the distance from the s
park plug to the end gases(by running on both plugs). And you can dilut
e the charge by adding water, excess fuel or excess air (run LOP). As y
ou can see, most of these things will reduce the power output of the eng
ine and therein lies the conundrum. For a standard unmodified aircraft
engine the worst operating case would be a takeoff from Death Valley on
a dry, 115-degree day with the carb heat left on, mixture leaned and one
of the mags inoperative. As I recall it is just those conditions that
the FAA requires to be demonstrated for a certified engine.Sorry about t
he excessively long non-electric dissertation.Gary Casey
The higher the octane rating, the higher the temperature and
pressure that can be reached before detonation occurs. I am not positive
on this, but am pretty certain on Mainland USA, the pump octane rating
is
not figured the same as Aviation fuel is, I forget if Avgas is higher or
lower. Anyway for a short time detonation probably will not cause any
real
harm. Now if you let it go on for long periods of time, things will
begin
to heat up, detonation will become more pronounced. The burning of fuel
mixture during Detonation begins with a spark at the plug. Preignition
is
the real show stopper. This is where for some reason the mixture ignites
way too far advanced. Could be a glowing piece of carbon, or leaving the
helicoil tab stick a bit too much into the cylinder, or just plain too
high a temperature. Piston moving up and fighting pressure now.
OK comments here??
OK so if we are straight that octane rating is the ability for a fuel to
not detonate, I don't think that is absolute takes into consideration
the
speed at which the flame front will burn in an orderly fashion.
Different
brews can have the same octane rating, but can burn at different speeds.
Ron Parigoris
========================
========================
========================
========================
========================
========================
====================
Thank you Gary. That is the best explanation of octane and deto
nation/ preignition scenerios I have ever read. I was going to try to de
srcibe it but you did so much better. The only thing I might add is the
fact that in the process of diluting the mixture with extra air there is
a point where before it really starts to run lean the engine flame fron
t goes into a blow torch effect and will melt the top of the piston and
or the exhaust valve. If you can transition though this setting fast eno
ugh the motor just lays down and the EGT's show a cooler number, set the
air/fuel mixture at around 16-1, depending on the engine of course
, and work the motor hard, you will get very high EGT's, low fuel f
low numbers and hurt pistons/ valves. The best way to describe
it is watch a cutting torch work, one adjusts the mixture till th
ey get a neutral flame and when you press the lever the additional
O2 will not only add to the velocity of the flame front , it will almost
double the temp of the cutting flame itself. .
Ben
www.haaspowerair.com
Ben Haas
N801BH
www.haaspo
werair.com
-- Gary Casey <glcasey(at)adelphia.net&
gt; wrote:
Good comments, Ron. Yes, the octane rating is a
measure of the resistance of the fuel/air mixture to auto-ignite, or ig
nite without the presence of an open flame. It's a complex phenome
non and autoignition is a function of time, pressure and temperature.&nb
sp; The rating methodology, developed by Ethyl Corporation way back when
, compares the resistance to auto-ignition of the test fuel to mixtures
of normal heptane to iso-octane. The octane number is the percenta
ge of iso-octane in the mix that behaves like the test fuel (80-octane f
uel behaves like a a mixture of 20% n-heptane and 80% iso-octane).
;Since the actual test is really done by measuring the BMEP of a test en
gine, numbers over 100 are possible - 110-octane fuel will allow the tes
t engine to operate at 110% of the BMEP allowed by iso-octane(not exactl
y correct, but close enough). The method isn't exact and if the te
st engine is operated at different temperatures and loads the observed o
ctane number comes out differently. Running at light load creates
an octane rating called the "research octane" number and running at high
temperature/high load produces a number called "motor octane". Th
e law says the average octane rating of an automotive fuel must be displ
ayed on the pump and that's why it says (R+M)/2 on the pump. Aviat
ion fuel, because engines are usually operated under conditions more lik
e the the motor method, are typically rated by the motor method - I beli
eve 100LL is more correctly called 100/120 (100 motor octane and 120 res
earch octane). That's why some of the past-history fuels were call
ed 110/130 etc.
When the fuel is ignited by an open flame front there is little dif
ference in flame speed between high octane and low octane fuel: Fl
ame speed is NOT the primary difference between the fuels. Detonat
ion is auto-ignition of the "end gases" late in the combustion process.
Because of combustion in the cylinder the end gases(the portion of
the charge furthest from the ignition source) are compressed to very hi
gh pressures, which because of the gas law PV=NRT, raises their temper
ature. They will only remain unburned for a limited time and if th
e flame front doesn't arrive soon enough, igniting them progressively, t
hey will auto-ignite all at once, "exploding." This will cause all
sorts of problems, but will not usually result in immediate engine fail
ure.
As Ron correctly described below, "pre-ignition" is simply ignition
of the fuel charge before the spark occurs. Because the charge bu
rns and raises the pressure before the piston fully compresses the charg
e the temperature and pressure can go to extremely high levels, causing
major damage very quickly. For example (George Braly would have th
e real numbers) normal compression (no ignition) pressure might be 350ps
i, combustion results in pressures of 800 to 1,000 psi and pre-ignition
could result in pressures up to 2,000 psi. Pre-ignition can (likel
y) result from pre-ignition because of the extremely high pressure and t
emperature of the end gases. One thing that isn't usually thought
about is the rate of heat transfer from a gas to the cylinder, which is
proportional to the velocity, temperature difference AND PRESSURE of the
gas. Double the pressure and double the temperature and the heat
transfer will go up by a factor of 4. Detonation results in sonic
shock waves traveling through the combustion chamber, which means locall
y the hot gases are moving at sonic velocity. Much of the damage f
rom both detonation and pre-ignition is caused by the extremely high hea
t transfer rates, not just the pressure. Detonation under high loa
ds can increase the local heat transfer rate to the point that after a s
hort time a component (edge of the exhaust valve, carbon deposit, etc) c
an be heated to the point it causes pre-ignition. This has sometim
es been referred to as "runaway detonation."
I hope from the above description you get the idea that detonation
and pre-ignition can be a real horror story for the engine. The be
st thing is to maintain a healthy detonation margin. In general, d
etonation is suppressed by increasing the octane rating, lowering the co
mpression ratio, retarding the ignition timing, lowering the inlet tempe
rature and pressure, lowering the cylinder head temperature, increasing
turbulence and reducing the distance from the spark plug to the end gase
s(by running on both plugs). And you can dilute the charge by addi
ng water, excess fuel or excess air (run LOP). As you can see, mos
t of these things will reduce the power output of the engine and therein
lies the conundrum. For a standard unmodified aircraft engine the
worst operating case would be a takeoff from Death Valley on a dry, 115
-degree day with the carb heat left on, mixture leaned and one of the ma
gs inoperative. As I recall it is just those conditions that the F
AA requires to be demonstrated for a certified engine.
Sorry about the excessively long non-electric dissertation.
Gary Casey
The higher the octane rating, the higher the temperature
and
pressure that can be reached before detonation occurs. I
am not positive
on this, but am pretty certain on Mainland USA, the pump
octane rating
is
not figured the same as Aviation fuel is, I forget if Av
gas is higher or
lower. Anyway for a short time detonation probably will
not cause any
real
harm. Now if you let it go on for long periods of time,
things will
begin
to heat up, detonation will become more pronounced. The
burning of fuel
mixture during Detonation begins with a spark at the plu
g. Preignition
is
the real show stopper. This is where for some reason the
mixture ignites
way too far advanced. Could be a glowing piece of carbon
, or leaving the
helicoil tab stick a bit too much into the cylinder, or
just plain too
high a temperature. Piston moving up and fighting pressu
re now.
OK comments here??
OK so if we are straight that octane rating is the abili
ty for a fuel to
not detonate, I don't think that is absolute takes into
consideration
the
speed at which the flame front will burn in an orderly f
ashion.
Different
brews can have the same octane rating, but can burn at d
ifferent speeds.
Ron Parigoris